The Experts below are selected from a list of 81 Experts worldwide ranked by ideXlab platform
Ganglong Cui - One of the best experts on this subject based on the ideXlab platform.
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Quantum Mechanics/Molecular Mechanics Studies on the Photophysical Mechanism of Methyl Salicylate.
The journal of physical chemistry. A, 2021Co-Authors: Xue-ping Chang, Teng-shuo Zhang, Ye-guang Fang, Ganglong CuiAbstract:Methyl salicylate (MS) as a subunit of larger salicylates found in commercial sunscreens has been shown to exhibit keto-enol tautomerization and dual fluorescence emission via excited-state intramolecular proton transfer (ESIPT) after the absorption of ultraviolet (UV) radiation. However, its excited-state relaxation mechanism is unclear. Herein, we have employed the quantum mechanics(CASPT2//CASSCF)/molecular mechanics method to explore the ESIPT and excited-state relaxation mechanism of MS in the lowest three electronic states, that is, S0, S1, and T1 states, in a methanol solution. Based on the optimized geometric and electronic structures, conical intersections and crossing points, and minimum-energy paths combined with the computed linearly interpolated Cartesian coordinate paths, the photophysical mechanism of MS has been proposed. The S1 state is a spectroscopically bright 1ππ* state in the Franck-Condon region. From the initially populated S1 state, there exist three nonradiative relaxation paths to repopulate the S0 state. In the first one, the S1 System (i.e., ketoB form) first undergoes an ESIPT path to generate an S1 tautomer (i.e., enol form) that exhibits a large Stokes shift in experiments. The generated S1 enol tautomer further evolves toward the nearby S1/S0 conical intersection and then hops to the S0 state, followed by the backward ground-state intramolecular proton transfer (GSIPT) to the initial ketoB form S0 state. In the second one, the S1 System first hops through the S1 → T1 interSystem crossing (ISC) to the T1 state, which then further decays to the S0 state via T1 → S0 ISC at the T1/S0 crossing point. In the third path, the T1 System that stems from the S1 → T1 ISC process via the S1/T1 crossing point first takes place a T1 ESIPT to generate a T1 enol tautomer, which can further decay to the S0 state via T1-to-S0 ISC. Finally, the GSIPT occurs to back the System to the initial ketoB form S0 state. Our present work could contribute to understanding the photophysics of MS and its derivatives.
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Selenium substitution effects on excited-state properties and photophysics of uracil: a MS-CASPT2 study.
Physical chemistry chemical physics : PCCP, 2020Co-Authors: Qin Peng, Teng-shuo Zhang, Xiang-yang Liu, Wei-hai Fang, Yun-hua Zhu, Ganglong CuiAbstract:The photophysics of selenium-substituted nucleobases has attracted recent experimental attention because they could serve as potential photosensitizers in photodynamic therapy. Herein, we present a comprehensive MS-CASPT2 study on the spectroscopic and excited-state properties, and photophysics of 2-selenouracil (2SeU), 4-selenouracil (4SeU), and 2,4-selenouracil (24SeU). Relevant minima, conical intersections, crossing points, and excited-state relaxation paths in the lowest five electronic states (i.e., S0, S1, S2, T2, and T1) are explored. On the basis of these results, their photophysical mechanisms are proposed. Upon photoirradiation to the bright S2 state, 2SeU quickly relaxes to its S2 minimum and then moves in an essentially barrierless way to a nearby S2/S1 conical intersection near which the S1 state is populated. Next, the S1 System arrives at an S1/T2/T1 intersection where a large S1/T1 spin–orbit coupling of 430.8 cm−1 makes the T1 state populated. In this state, a barrier of 6.8 kcal mol−1 will trap 2SeU for a while. In parallel, for 4SeU or 24SeU, the System first relaxes to the S2 minimum and then overcomes a small barrier to approach an S2/S1 conical intersection. Once hopping to the S1 state, there exists an extended region with very close S1, T2, and T1 energies. Similarly, a large S1/T1 spin–orbit coupling of 426.8 cm−1 drives the S1 → T1 interSystem crossing process thereby making the T1 state populated. Similarly, an energy barrier heavily suppresses electronic transition to the S0 state. The present work manifests that different selenium substitutions on uracil can lead to a certain extent of different vertical and adiabatic excitation energies, excited-state properties, and relaxation pathways. These insights could help understand the photophysics of selenium-substituted nucleobases.
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Photochemical mechanism of 1,5-benzodiazepin-2-one: electronic structure calculations and nonadiabatic surface-hopping dynamics simulations
Physical chemistry chemical physics : PCCP, 2019Co-Authors: Shu-hua Xia, Yan Liu, Yan Zhang, Meng Che, Ganglong CuiAbstract:Due to the significant applications in bioimaging, sensing, optoelectronics etc., photoluminescent materials have attracted more and more attention in recent years. 1,5-Benzodiazepin-2-one and its derivatives have been used as fluorogenic probes for the detection of biothiols. However, their photochemical and photophysical properties have remained ambiguous until now. In this work, we have adopted combined static electronic structure calculations and nonadiabatic surface-hopping dynamics simulations to study the photochemical mechanism of 1,5-benzodiazepin-2-one. Firstly, we optimized minima and conical intersections in S0 and S1 states; then, we proposed three nonadiabatic decay pathways that efficiently populate the ground state from the Franck–Condon region based on computed electronic structure information and dynamics simulations. In the first pathway, upon photoexcitation to the S1 state, the System proceeds with an ultrafast excited-state intramolecular proton transfer (ESIPT) process. Then, the molecule tends to rotate around the C–C bond until it encounters keto conical intersections, from which the System can easily decay to the ground state. The other two pathways involve the enol channels in which the S1 System hops to the ground state via two enol S1/S0 conical intersections, respectively. These three energetically allowed S1 excited-state deactivation pathways are responsible for the decrease of fluorescence quantum yield. The present work will provide detailed mechanistic information of similar Systems.
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A theoretical study of the light-induced cross-linking reaction of 5-fluoro-4-thiouridine with thymine
Physical chemistry chemical physics : PCCP, 2017Co-Authors: Xue-ping Chang, Pin Xiao, Juan Han, Wei-hai Fang, Ganglong CuiAbstract:In contrast to photophysics of thio-substituted nucleobases, their photoinduced cross-linking reactions with canonical nucleobases remain scarcely investigated computationally. In this work, we have adopted combined CASPT2/PCM//CASSCF and B3LYP-D3/PCM electronic structure methods to study this kind of photochemical reaction of 5-fluoro-4-thiouridine (truncated 5-fluoro-1-methyl-4-thiouracil used in calculations) and 1-methylthymine (referred to as thymine for clarity hereinafter). On the basis of CASPT2/PCM computed results, we have proposed two efficient excited-state relaxation pathways to populate the lowest T1 state of the complex of 5-fluoro-1-methyl-4-thiouracil and thymine from its initially populated S2(1ππ*) state. In the first one, the S2 System first hops to the S1 state via an S2/S1 conical intersection, followed by a direct S1 → T1 interSystem crossing process enhanced by large S1/T1 spin–orbit coupling. In the second path, the resultant S1 System first jumps to the T2 state, from which an efficient T2 → T1 internal conversion occurs. The T1 cross-linking reaction is overall divided into two phases. The first phase is a stepwise and nonadiabatic photocyclization reaction, which starts from the T1 complex and ends up with an S0 thietane intermediate. The second phase is a thermal reaction. The System first rearranges its four- and six-membered rings to form three new rings; then, an S0 fluorine atom transfer occurs, followed by the formation of photoproducts. Finally, the present work paves the way for studying light-induced cross-linking reactions of thionucleobases with canonical bases in DNA and RNA.
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Excited-State Intramolecular Proton Transfer in a Blue Fluorescence Chromophore Induces Dual Emission.
Chemphyschem : a European journal of chemical physics and physical chemistry, 2016Co-Authors: Wei-wei Guo, Xiang-yang Liu, Ganglong CuiAbstract:Compared with green fluorescence protein (GFP) chromophores, the recently synthesized blue fluorescence protein (BFP) chromophore variant presents intriguing photochemical properties, for example, dual fluorescence emission, enhanced fluorescence quantum yield, and ultra-slow excited-state intramolecular proton transfer (ESIPT; J. Phys. Chem. Lett., 2014, 5, 92); however, its photochemical mechanism is still elusive. Herein we have employed the CASSCF and CASPT2 methods to study the mechanistic photochemistry of a truncated BFP chromophore variant in the S0 and S1 states. Based on the optimized minima, conical intersections, and minimum-energy paths (ESIPT, photoisomerization, and deactivation), we have found that the System has two competitive S1 relaxation pathways from the Franck-Condon point of the BFP chromophore variant. One is the ESIPT path to generate an S1 tautomer that exhibits a large Stokes shift in experiments. The generated S1 tautomer can further evolve toward the nearby S1 /S0 conical intersection and then jumps down to the S0 state. The other is the photoisomerization path along the rotation of the central double bond. Along this path, the S1 System runs into an S1 /S0 conical intersection region and eventually hops to the S0 state. The two energetically allowed S1 excited-state deactivation pathways are responsible for the in-part loss of fluorescence quantum yield. The considerable S1 ESIPT barrier and the sizable barriers that separate the S1 tautomers from the S1 /S0 conical intersections make these two tautomers establish a kinetic equilibrium in the S1 state, which thus results in dual fluorescence emission.
Xue-ping Chang - One of the best experts on this subject based on the ideXlab platform.
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Quantum Mechanics/Molecular Mechanics Studies on the Photophysical Mechanism of Methyl Salicylate.
The journal of physical chemistry. A, 2021Co-Authors: Xue-ping Chang, Teng-shuo Zhang, Ye-guang Fang, Ganglong CuiAbstract:Methyl salicylate (MS) as a subunit of larger salicylates found in commercial sunscreens has been shown to exhibit keto-enol tautomerization and dual fluorescence emission via excited-state intramolecular proton transfer (ESIPT) after the absorption of ultraviolet (UV) radiation. However, its excited-state relaxation mechanism is unclear. Herein, we have employed the quantum mechanics(CASPT2//CASSCF)/molecular mechanics method to explore the ESIPT and excited-state relaxation mechanism of MS in the lowest three electronic states, that is, S0, S1, and T1 states, in a methanol solution. Based on the optimized geometric and electronic structures, conical intersections and crossing points, and minimum-energy paths combined with the computed linearly interpolated Cartesian coordinate paths, the photophysical mechanism of MS has been proposed. The S1 state is a spectroscopically bright 1ππ* state in the Franck-Condon region. From the initially populated S1 state, there exist three nonradiative relaxation paths to repopulate the S0 state. In the first one, the S1 System (i.e., ketoB form) first undergoes an ESIPT path to generate an S1 tautomer (i.e., enol form) that exhibits a large Stokes shift in experiments. The generated S1 enol tautomer further evolves toward the nearby S1/S0 conical intersection and then hops to the S0 state, followed by the backward ground-state intramolecular proton transfer (GSIPT) to the initial ketoB form S0 state. In the second one, the S1 System first hops through the S1 → T1 interSystem crossing (ISC) to the T1 state, which then further decays to the S0 state via T1 → S0 ISC at the T1/S0 crossing point. In the third path, the T1 System that stems from the S1 → T1 ISC process via the S1/T1 crossing point first takes place a T1 ESIPT to generate a T1 enol tautomer, which can further decay to the S0 state via T1-to-S0 ISC. Finally, the GSIPT occurs to back the System to the initial ketoB form S0 state. Our present work could contribute to understanding the photophysics of MS and its derivatives.
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A theoretical study of the light-induced cross-linking reaction of 5-fluoro-4-thiouridine with thymine
Physical chemistry chemical physics : PCCP, 2017Co-Authors: Xue-ping Chang, Pin Xiao, Juan Han, Wei-hai Fang, Ganglong CuiAbstract:In contrast to photophysics of thio-substituted nucleobases, their photoinduced cross-linking reactions with canonical nucleobases remain scarcely investigated computationally. In this work, we have adopted combined CASPT2/PCM//CASSCF and B3LYP-D3/PCM electronic structure methods to study this kind of photochemical reaction of 5-fluoro-4-thiouridine (truncated 5-fluoro-1-methyl-4-thiouracil used in calculations) and 1-methylthymine (referred to as thymine for clarity hereinafter). On the basis of CASPT2/PCM computed results, we have proposed two efficient excited-state relaxation pathways to populate the lowest T1 state of the complex of 5-fluoro-1-methyl-4-thiouracil and thymine from its initially populated S2(1ππ*) state. In the first one, the S2 System first hops to the S1 state via an S2/S1 conical intersection, followed by a direct S1 → T1 interSystem crossing process enhanced by large S1/T1 spin–orbit coupling. In the second path, the resultant S1 System first jumps to the T2 state, from which an efficient T2 → T1 internal conversion occurs. The T1 cross-linking reaction is overall divided into two phases. The first phase is a stepwise and nonadiabatic photocyclization reaction, which starts from the T1 complex and ends up with an S0 thietane intermediate. The second phase is a thermal reaction. The System first rearranges its four- and six-membered rings to form three new rings; then, an S0 fluorine atom transfer occurs, followed by the formation of photoproducts. Finally, the present work paves the way for studying light-induced cross-linking reactions of thionucleobases with canonical bases in DNA and RNA.
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Mechanistic photodecarboxylation of pyruvic acid: excited-state proton transfer and three-state intersection.
The Journal of chemical physics, 2014Co-Authors: Xue-ping Chang, Qiu Fang, Ganglong CuiAbstract:Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S0, T1, and S1 states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S1 System relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S1/S0 conical intersection funnels the S1 to S0 state. Then, some trajectories continue completing the decarboxylation reaction in the S0 state; the remaining trajectories via a reverse hydrogen transfer return to the S0 minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S1 −T1 energy gap and a large S1/T1 spin-orbit coupling, an efficient S1 → T1 interSystem crossing process happens again near this S1/S0 conical intersection. When decaying to T1 state, a direct photodecarboxylation proceeds. (iii) Prior to ESIPT, the S1 System first decays to the T1 state via an S1 → T1 interSystem crossing; then, the T1 System evolves to a hydrogen-transferred tautomer. Therefrom, an adiabatic T1 decarboxylation takes place due to a small barrier of 7.7 kcal/mol. (iv) Besides the aforementioned T1 ESIPT process, there also exists a comparable Norrish type I reaction in the T1 state, which forms the ground-state products of CH3CO and COOH. Finally, we have found that ESIPT plays an important role. It closes the S1-T1 and S1-S0 energy gaps, effecting an S1/T1/S0 three-state intersection region, and mediating nonadiabatic photodecarboxylation reactions of pyruvic acid.
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mechanistic photodecarboxylation of pyruvic acid excited state proton transfer and three state intersection
Journal of Chemical Physics, 2014Co-Authors: Xue-ping Chang, Qiu FangAbstract:Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S0, T1, and S1 states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S1 System relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S1/S0 conical intersection funnels the S1 to S0 state. Then, some trajectories continue completing the decarboxylation reaction in the S0 state; the remaining trajectories via a reverse hydrogen transfer return to the S0 minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S1 −T1 energy gap and a large S1/T1 spin-orbit coupling, an efficient S1 → T1 interSystem crossing process happens again near this S1/S0 conical intersection. When decaying to T1 state, a direct photodecarboxylation proceed...
Qiu Fang - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic photodecarboxylation of pyruvic acid: excited-state proton transfer and three-state intersection.
The Journal of chemical physics, 2014Co-Authors: Xue-ping Chang, Qiu Fang, Ganglong CuiAbstract:Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S0, T1, and S1 states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S1 System relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S1/S0 conical intersection funnels the S1 to S0 state. Then, some trajectories continue completing the decarboxylation reaction in the S0 state; the remaining trajectories via a reverse hydrogen transfer return to the S0 minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S1 −T1 energy gap and a large S1/T1 spin-orbit coupling, an efficient S1 → T1 interSystem crossing process happens again near this S1/S0 conical intersection. When decaying to T1 state, a direct photodecarboxylation proceeds. (iii) Prior to ESIPT, the S1 System first decays to the T1 state via an S1 → T1 interSystem crossing; then, the T1 System evolves to a hydrogen-transferred tautomer. Therefrom, an adiabatic T1 decarboxylation takes place due to a small barrier of 7.7 kcal/mol. (iv) Besides the aforementioned T1 ESIPT process, there also exists a comparable Norrish type I reaction in the T1 state, which forms the ground-state products of CH3CO and COOH. Finally, we have found that ESIPT plays an important role. It closes the S1-T1 and S1-S0 energy gaps, effecting an S1/T1/S0 three-state intersection region, and mediating nonadiabatic photodecarboxylation reactions of pyruvic acid.
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mechanistic photodecarboxylation of pyruvic acid excited state proton transfer and three state intersection
Journal of Chemical Physics, 2014Co-Authors: Xue-ping Chang, Qiu FangAbstract:Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S0, T1, and S1 states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S1 System relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S1/S0 conical intersection funnels the S1 to S0 state. Then, some trajectories continue completing the decarboxylation reaction in the S0 state; the remaining trajectories via a reverse hydrogen transfer return to the S0 minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S1 −T1 energy gap and a large S1/T1 spin-orbit coupling, an efficient S1 → T1 interSystem crossing process happens again near this S1/S0 conical intersection. When decaying to T1 state, a direct photodecarboxylation proceed...
Chris Wilson - One of the best experts on this subject based on the ideXlab platform.
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formal verification of the hal S1 System cache coherence protocol
International Conference on Computer Design, 1997Co-Authors: M Fujita, Chris WilsonAbstract:The paper describes the authors' experience applying formal verification to the cache coherence protocol of the HAL S1 System, a shared-memory and/or message-passing multiprocessor consisting of standard Intel Pentium/sup (R/) Pro symmetric multiprocessing (SMP) servers connected by HAL's proprietary Mercury Interconnect to create a cache-coherent, non-uniform memory access (CC-NUMA) machine. In recent years, several researchers have described the verification of cache coherence protocols to demonstrate the potential of formal verification. In this project, they sought to quantify this potential by carefully tracking the effort and results of applying formal verification, rather than simply demonstrating that verification was possible. Based on their records and experience, they show that protocol-level formal verification, properly applied, is sufficiently well-understood to be routinely undertaken, and they describe the techniques used to simplify the verification process. On the negative side, their formal verification methodology has limitations, so they outline the pitfalls encountered and recommend ways to minimize them.
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ICCD - Formal verification of the HAL S1 System cache coherence protocol
Proceedings International Conference on Computer Design VLSI in Computers and Processors, 1Co-Authors: M Fujita, Chris WilsonAbstract:The paper describes the authors' experience applying formal verification to the cache coherence protocol of the HAL S1 System, a shared-memory and/or message-passing multiprocessor consisting of standard Intel Pentium/sup (R/) Pro symmetric multiprocessing (SMP) servers connected by HAL's proprietary Mercury Interconnect to create a cache-coherent, non-uniform memory access (CC-NUMA) machine. In recent years, several researchers have described the verification of cache coherence protocols to demonstrate the potential of formal verification. In this project, they sought to quantify this potential by carefully tracking the effort and results of applying formal verification, rather than simply demonstrating that verification was possible. Based on their records and experience, they show that protocol-level formal verification, properly applied, is sufficiently well-understood to be routinely undertaken, and they describe the techniques used to simplify the verification process. On the negative side, their formal verification methodology has limitations, so they outline the pitfalls encountered and recommend ways to minimize them.
Shu-hua Xia - One of the best experts on this subject based on the ideXlab platform.
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Photochemical and photophysical properties of cis-stilbene molecule by electronic structure calculations and nonadiabatic surface-hopping dynamics simulations
Chemical Physics, 2020Co-Authors: Yan Liu, Shu-hua Xia, Yan ZhangAbstract:Abstract We combined the electronic structure calculations and OM2(orthogonalization model 2)/MRCI nonadiabatic surface-hopping dynamics simulations to scrutinize the photoisomerization mechanisms of cis-stilbene. The static electronic structure calculations showed that the irradiation of cis-stilbene populates the bright S1 state and we obtained three S1/S0 conical intersections (CIs) and proposed two nonadiabatic decay channels that efficiently de-excited to the ground state. In the first pathway, once excited to the S1 state, the cis-stilbene proceeds along S1 potential energy surface. Then, the molecule encounters S1S0-C CI, from which the System decays to S0 state. The other pathway involves the S1S0-D CI from where the S1 System hops to the ground state. In our simulations, we acquired cis, trans and DHP (4a,4b-dihydrophenanthrene) products and the ratio is estimated as 42:48:7. The present work show that the combination of electronic structure calculations and OM2/MRCI nonadiabatic dynamics can give detailed photochemical and photophysical information of stilbene Systems.
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Photochemical mechanism of 1,5-benzodiazepin-2-one: electronic structure calculations and nonadiabatic surface-hopping dynamics simulations
Physical chemistry chemical physics : PCCP, 2019Co-Authors: Shu-hua Xia, Yan Liu, Yan Zhang, Meng Che, Ganglong CuiAbstract:Due to the significant applications in bioimaging, sensing, optoelectronics etc., photoluminescent materials have attracted more and more attention in recent years. 1,5-Benzodiazepin-2-one and its derivatives have been used as fluorogenic probes for the detection of biothiols. However, their photochemical and photophysical properties have remained ambiguous until now. In this work, we have adopted combined static electronic structure calculations and nonadiabatic surface-hopping dynamics simulations to study the photochemical mechanism of 1,5-benzodiazepin-2-one. Firstly, we optimized minima and conical intersections in S0 and S1 states; then, we proposed three nonadiabatic decay pathways that efficiently populate the ground state from the Franck–Condon region based on computed electronic structure information and dynamics simulations. In the first pathway, upon photoexcitation to the S1 state, the System proceeds with an ultrafast excited-state intramolecular proton transfer (ESIPT) process. Then, the molecule tends to rotate around the C–C bond until it encounters keto conical intersections, from which the System can easily decay to the ground state. The other two pathways involve the enol channels in which the S1 System hops to the ground state via two enol S1/S0 conical intersections, respectively. These three energetically allowed S1 excited-state deactivation pathways are responsible for the decrease of fluorescence quantum yield. The present work will provide detailed mechanistic information of similar Systems.
